As a mode of directly obtaining an AC output voltage from an AC power supply, a mode using a direct AC power conversion device typified by a matrix converter is known. The direct AC power conversion device can be expected to be miniaturized and to enhance efficiency thereof, and accordingly, has attracted attention as a next-generation power conversion device. However, the matrix converter is in a course of being popularized since a main circuit configuration and modulation method thereof are special.
In contrast, there has been proposed a modulation mode using an indirect method of using an indirect conversion device that is a mainstream at present and connecting an AC/DC converter (hereinafter, simply referred to as “converter”) and a DC/AC inverter (hereinafter, simply referred to as “inverter”) to each other by a DC link (for example, L. Wei, T. A. Lipo, “A Novel Matrix Converter Topology with Simple Commutation”, IEEE IAS2001, voL9, pp. 1749-1754(2001)).
The indirect method has already been put into practical use as an air conditioner (for example, Fujita, Sakakibara, Matsuno, “Application and Development of the Three Phase Indirect Matrix Converter for Air Conditioners”, The Institute of Electrical Engineers of Japan, The papers of Joint Technical Meeting on Semiconductor Power Converter/Vehicle Technology/Home and Consumer Appliances, SPC-12-174/VT-12-025/HCA-12-059, IEE Japan 2012 (20), pp. 31-36, 2012-12-06) by technological development such as a modulation mode suitable for a consumer microcomputer (for example, Japanese Patent No. 4135026) and a simplification of a main circuit (for example, Japanese Patent No. 4049189). Moreover, application of the indirect method to a single-phase instrument has also been studied by combining an active buffer added with a charging circuit (for example, Ohnuma, Itoh, “Circuit Configuration and Control Strategy of single-to-three Phase Power Converter with Active Buffer and Charging Circuit”, The 2010 Annual Meeting of The Institute of Electrical Engineers of Japan, 4-057 (2010) and Japanese Patent Application Laid-Open No. 2011-193678).
Meanwhile, in order to simplify a current sensor, to the indirect conversion device, there is applied a method of detecting a current by DC link by means of a shunt resistor and detecting a phase current on the basis of a switching pattern of an inverter circuit. In order to apply this method, it is necessary to hold the switching pattern for a period longer than both a delay of the current detection and a dead time period.
There has been proposed a technology for extending and maintaining a switching pattern for the purpose of detecting a current, when the switching pattern to be originally adopted is short. In order to reduce a distortion occurring in an output due to such extension, there has also been proposed a technology for correcting a vector pattern, which corresponds to the switching pattern, by another vector pattern (for example, Japanese Patent Application Laid-Open No. H03-230767).
In such a direct conversion device, one cycle of a carrier is divided by an intermediate phase of a command voltage of a current source converter. Then, in each of these divided periods, the same switching pattern is adopted. Hence, it has also been proposed to detect the current in a longer one of the divided periods (for example, Japanese Patent No. 5167869).
Note that Japanese Patent Application Laid-Open No. 2013-93992 is cited as a document that discloses a technology related to the present application.